US20030202554A1 - Laser resonator - Google Patents

Laser resonator Download PDF

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US20030202554A1
US20030202554A1 US10/329,471 US32947102A US2003202554A1 US 20030202554 A1 US20030202554 A1 US 20030202554A1 US 32947102 A US32947102 A US 32947102A US 2003202554 A1 US2003202554 A1 US 2003202554A1
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Prior art keywords
laser
telescope
laser beam
resonator
reflecting means
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US6853670B2 (en
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Takayuki Yanagisawa
Yoshihito Hirano
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Mitsubishi Electric Corp
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Mitsubishi Electric Corp
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/08—Construction or shape of optical resonators or components thereof
    • H01S3/08018—Mode suppression
    • H01S3/0804—Transverse or lateral modes
    • H01S3/08045—Single-mode emission
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/08—Construction or shape of optical resonators or components thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/08—Construction or shape of optical resonators or components thereof
    • H01S3/08018—Mode suppression
    • H01S3/0804—Transverse or lateral modes
    • H01S3/0805—Transverse or lateral modes by apertures, e.g. pin-holes or knife-edges
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/08—Construction or shape of optical resonators or components thereof
    • H01S3/08059—Constructional details of the reflector, e.g. shape
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/08—Construction or shape of optical resonators or components thereof
    • H01S3/08072—Thermal lensing or thermally induced birefringence; Compensation thereof

Definitions

  • the present invention relates to a laser resonator which is used in, for example, a solid laser device installed in airports or the like, or a solid laser device mounted in trajectory bodies such as artificial satellites or aircrafts, and more particularly which requires a long resonance length for a pulse type coherent lidar (laser rader) for measuring the wind velocity or the like.
  • a pulse type coherent lidar laser rader
  • the wavelength in the range of 1.4 ⁇ m to 2.0 ⁇ m which is safe for human eyes is required.
  • the laser material for oscillating with this eye safe wavelength for example, there have been well known Er: Glass (the oscillation wavelength is 1.5 ⁇ m), Er, Yb: Glass (the oscillation wavelength is 1.5 ⁇ m), Er: YAG (the oscillation wavelength is 1.6 ⁇ m), Tm: YAG (the oscillation wavelength is 2 ⁇ m), Tm, Ho: YAG (the oscillation wavelength is 2 ⁇ m), Ho: YLF (the oscillation wavelength is 2 ⁇ m), Tm, Ho: YLF (the oscillation wavelength is 2 ⁇ m), and the like.
  • the gain inherent in the material is small.
  • a loss to a propagation mode in the laser resonator can be described qualitatively using a Fresnel number N represented by a smallest aperture radius “a” in the resonator and a resonator length L.
  • the Fresnel number N is defined by the following expression:
  • FIG. 23 shows a relationship between the Fresnel number N and a loss given to the propagation mode in the laser resonator, which is described in “Springer Series in Optical Sciences Vol. 1 ‘Solid-State Laser Engineering Ver. 4’ Walter Koechner (1995, Springer, Germany), page 202”.
  • the Fresnel number decreases, the loss given to the propagation mode increases.
  • a loss generated due to a transmissivity of optical components, or the like of a general laser resonator is in the order of several percent to 10%.
  • a loss given to a basic mode (TEM00 mode) that is least affected by a loss increases to the same degree as other losses, whereby fall in an output occurs and it becomes difficult to obtain stable laser oscillation.
  • FIG. 18 is a schematic view showing the construction of a conventional laser resonator which, for example, is shown in an article of “Springer Series in Optical Science”, by Walter Koechner, Solid-state laser engineering, 4th edition (Springer, Germany, 1995, pp. 197), and an article of “LASERS”, by Siegman (University Science Books, U.S.A., 1986), pp. 755.
  • reference numerals 1 and 2 denote concave reflecting mirrors which are arranged at a distance of the resonator L in such a way as to face each other to confine therein a laser beam
  • reference numeral 3 denotes a laser material
  • reference numeral 4 denotes an excitation light source for exciting the laser material 3
  • reference numeral 5 denotes a resonance mode of the Gaussian beam which is defined between the concave reflecting mirrors 1 and 2
  • reference numeral 6 denotes an aperture for limiting the resonance mode
  • reference numeral 7 denotes an optical axis.
  • the laser beam makes a round trip between the concave reflecting mirrors 1 and 2 to pass repeatedly through the laser material 3 which is excited by the pump light source 4 to be optically amplified, thereby forming the resonance modes 5 of the Gaussian beam.
  • the aperture 6 is arranged in order to select only the low-order mode of the resonance mode 5 to generate the laser beam of high quality.
  • the aperture of the optical component for the laser material 3 and the mirrors which are arranged within the laser resonator may be employed in some cases.
  • the beam size ⁇ 0 in the position where the beam size of the resonance mode 5 becomes the smallest is decreased the smaller the resonance length L, and also as smaller the value of 2 ⁇ R ⁇ L.
  • the position of ⁇ 0 where the beam size becomes the smallest becomes the center of the laser resonator, i.e., the position which is L/2 away from the concave reflecting mirror 1 . From Expression (4), in order to obtain the small ⁇ 0 , there are required the short resonance length L and the concave reflecting mirror having the curvature R with which the value of 2 ⁇ R ⁇ L becomes small.
  • FIG. 19 shows the relationship between the curvature R of the concave reflecting mirror, and ⁇ 0 and ⁇ 1 when the resonance length L is set to 2 m.
  • the curvature R with which the value of ⁇ 0 equal to or smaller than 0.25 mm is obtained is in the range of 1.017 m to 1.000 m, and the value of ⁇ 1 at this time is in the range of 1.92 mm to . Therefore, when the beam size is made to be small, the allowable range of the curvature R is narrow and also the beam size ⁇ 0 becomes sensitive to the change in the curvature R and the resonator length L. In addition thereto, the operation of the resonator becomes easily unstable, and hence the adjustment thereof becomes difficult. Also, since when the resonator length L is made longer with the same beam size, the operation of the resonator becomes further unstable, thus it is impossible to make the resonator length L sufficiently long.
  • a size of the laser material 3 is set such that the aperture size “a” is approximately 1.5 times as large as the beam size ⁇ 0 .
  • the Fresnel number N of this conventional laser resonator is 0.047. In this case, from FIG. 23, a large loss to the basic mode is generated and it becomes difficult to obtain stable laser oscillation.
  • FIG. 20 is a schematic view showing the situation of the resonance beam mode when an inclination ⁇ occurs in the concave reflecting mirror 1 .
  • the misalignment occurs between the optical axis of the resonance mode and the optical axis 7 of the laser resonator.
  • FIG. 21 also shows the relationship between the curvature R of the concave reflecting mirror, and ⁇ 0 and ⁇ 1 shown in FIG. 19.
  • the deviation angle ⁇ 0 in the central position of the resonator is increased as the curvature R of the concave reflecting mirror 1 approaches 1.
  • ⁇ 0 0.25 mm
  • the resonance mode in the position of the concave reflecting mirror 1 is deviated, the eclipse of the apertures of the optical components arranged in the aperture 6 and on the optical axis occurs, the laser output is decreased and also the quality of the laser beam is degraded.
  • the beam size ⁇ 1 in the position of the concave reflecting mirror 1 is 1.92 mm.
  • the resonance mode 5 is perfectly refused by the aperture 6 , therefore the resonance mode cannot be formed and the laser output cannot be obtained.
  • the slight inclination of the concave reflecting mirror gives the optical axis of the resonance mode within the resonator a large inclination so that the stability in the emission direction of the outputted laser beam is reduced.
  • a polarizer needs to be arranged on the optical path.
  • the degradation of the extinction ratio of the polarizer occurs depending on the incident angle of the laser beam. For this reason, when the angular deviation of the laser beam is large, a part of the laser beam is outputted to the outside by the polarizer so that the efficiency of utilizing the laser beam is reduced.
  • the birefringent material such as the EO-Q switch
  • the birefringent material changes the polarization of the laser beam depending on the incident angle of the laser beam. Therefore, there arises the problem that the resonance cannot be carried out as the laser beam and hence the efficiency of utilizing the laser beam is reduced.
  • the present invention has been made in order to solve the problems associated with the prior art, and it is therefore an object of the present invention to provide a laser resonator in which a small beam size can be stably obtained in a long resonator length, the reduction of the efficiency of utilizing a laser beam and the quality of the laser beam can be prevented, and the emission direction of the laser beam can be stabilized.
  • a laser resonator comprises: a laser material for being excited by a light source to amplify optically a laser beam; a first telescope for magnifying the laser beam which has been made incident from the laser material and for reducing the laser beam which has been made incident from the opposite side to the side of the laser material; first reflecting means for reflecting the laser beam, which has been made incident from the first telescope in the direction opposite to the incident direction; a second telescope which is arranged in such a way as to face the first telescope with the laser material sandwiched between the first telescope and the second telescope and which serves to magnify the laser beam which has been reflected by the first reflected means to be reduced by the first telescope and to be amplified by the laser material to be made incident thereto and also serves to reduce the laser beam which has been made incident from the opposite side to the side of the laser material; and second reflecting means which is arranged in such a way as to face the first reflecting means with the laser material sandwiched between the first reflecting means and the second reflecting means
  • a laser resonator comprises: a laser material for being excited by a light source to amplify optically a laser beam; a telescope for magnifying the laser beam which has been made incident from the laser material and for reducing the laser beam which has been made incident from the opposite side to the side of the laser material; first reflecting means for reflecting the laser beam, which has been made incident from the first telescope in the direction opposite to the incident direction; second reflecting means which is arranged in such a way as to face the first reflecting means with the laser material sandwiched between the first reflecting means and the second reflecting means and which serves to reflect the laser beam, which has been reflected by the first reflecting means to be reduced by the telescope and to be amplified by the laser material to be made incident thereto, in the opposite direction to the incident direction, wherein a magnification of said telescope is set such that a loss to a lower mode decreases and a loss to a higher mode increases in the resonator.
  • a laser resonator comprises: a laser material for being excited by a light source to amplify optically a laser beam; a first telescope for magnifying the laser beam which has been made incident from the laser material and for reducing the laser beam which has been made incident from the opposite side to the side of the laser material; a second telescope for magnifying the laser beam which has been made incident from the first telescope and for reducing the laser beam which has been made incident from the opposite side to the side of the first telescope; first reflecting means for reflecting the laser beam, which has been made incident from the second telescope, in the opposite direction to the incident direction; a third telescope which is arranged in such a way as to face the first telescope with the laser material sandwiched between the first telescope and the second telescope and which serves to magnify the laser beam which has been reflected by the first reflecting means to be reduced by the first and second telescopes and to be amplified by the laser material to be made incident thereto and also serves to reduce the laser beam which has been made incident from the opposite
  • FIG. 1 is a schematic view showing the construction of a laser resonator according to a first embodiment of the present invention
  • FIG. 2 is a graphical representation explaining the beam size of the laser resonator according to the first embodiment of the present invention
  • FIG. 3 is a graphical representation explaining the beam size when the laser resonator according to the first embodiment of the present invention is not symmetrical with the resonator as the center;
  • FIG. 4 is a schematic view showing the resonance mode when plane reflecting mirror of the laser resonator according to the first embodiment of the present invention is inclined;
  • FIG. 5 is a graphical representation explaining the misalignment amount between an optical axis of the laser resonator shown in FIG. 4 and the axis of the resonance mode;
  • FIG. 6 is a graphical representation explaining the misalignment angle between the optical axis of the laser resonator of FIG. 4 and the axis of the resonance mode;
  • FIG. 7 is a graphical representation explaining the misalignment amount between the beam size and the optical axis when changing a distance between a telescope of the laser resonator of FIG. 4 and a center of the resonator;
  • FIG. 8 is a graphical representation explaining the deviation angle of the optical axis when changing the distance between the telescope of the laser resonator of FIG. 4 and the center of the resonator;
  • FIG. 9 is a schematic view showing one example of a telescope of the laser resonator according to the first embodiment of the present invention.
  • FIG. 10 is a schematic view showing the construction of a laser resonator according to a second embodiment of the present invention.
  • FIG. 11 is a schematic view showing the construction of a laser resonator according to a third embodiment of the present invention.
  • FIG. 12 is a schematic view showing the construction of a laser resonator according to a fourth embodiment of the present invention.
  • FIG. 13 is a schematic view showing the construction of a laser resonator according to a fifth embodiment of the present invention.
  • FIG. 14 is a schematic view showing the reflection state of a laser beam which is made incident to a rood prism of the laser resonator according to the fifth embodiment of the present invention.
  • FIG. 15 is a schematic view showing the state in which the rood prism of the laser resonator according to the fifth embodiment of the present invention is inclined;
  • FIG. 16 is a schematic view showing the construction of a laser resonator according to a sixth embodiment of the present invention.
  • FIG. 17 is a schematic view showing another construction of the laser resonator according to a sixth embodiment of the present invention.
  • FIG. 18 is a schematic view showing the construction of a conventional laser resonator
  • FIG. 19 is a graphical representation explaining the beam size of the conventional laser resonator
  • FIG. 20 is a schematic view showing the resonance mode when a concave reflecting mirror of the conventional laser resonator is inclined;
  • FIG. 21 is a graphical representation explaining the misalignment amount between an optical axis of the laser resonator shown in FIG. 20 and an axis of the resonance mode;
  • FIG. 22 is a graphical representation explaining the misalignment angle between the optical axis of the laser resonator shown in FIG. 20 and the axis of the resonance mode;
  • FIG. 23 is a graph showing a relationship between the Fresnel number N and a loss given to the propagation mode in the laser resonator, which is described in “Springer Series in Optical Sciences Vol. 1 ‘Solid-State Laser Engineering Ver. 4’ Walter Koechner (1995, Springer, Germany), page 202”.
  • FIG. 1 is a schematic view showing the construction of a laser resonator according to Embodiment 1 of the present invention.
  • the same or corresponding parts are denoted with the same reference numerals.
  • reference numerals 11 and 12 denote plane reflecting mirrors, respectively; reference numeral 13 denotes a laser material; reference numeral 14 denotes a pump light source for exciting the laser material 13 ; reference numeral 15 denotes a telescope having lenses 15 a and 15 b ; reference numeral 16 denotes a telescope having lenses 16 a and 16 b ; reference numeral 17 denotes a resonance mode within a laser resonator; and reference numeral 18 denotes an aperture for limiting the resonance mode 17 .
  • the plane reflecting mirrors 11 and 12 are arranged in a symmetrical style with the laser material 13 as the center.
  • the telescope 15 is arranged between the plane reflecting mirror 11 and the laser material 13 .
  • a focal length of the lens 15 a of the telescope 15 is f 1
  • a focal length of the lens 15 b of the telescope 15 is f 2
  • an interval between the lends 15 a and the lends 15 b is f 1 +f 2 + ⁇ .
  • >1 is established.
  • the same optical component is employed for the telescope 15 and the telescope 16 which are in turn arranged symmetrically with the laser material 13 as the center.
  • the lens 15 a and the plane reflecting mirror 1 , and the lens 16 a and the plane reflecting mirror 12 are arranged in such a way that a distance between the lens 15 a and the plane reflecting mirror 1 and a distance between the lens 16 a and the plane reflecting mirror 12 becomes each L 1 .
  • the laser beam which has been emitted in the direction towards the telescope 15 through the laser material 13 is magnified by the telescope 15 to be propagated to be reflected in the opposite direction to the incident laser beam by the plane reflecting mirror 11 . Then, the laser beam which has been reflected by the plane reflecting mirror 11 is reduced by the telescope 15 to be made incident to the laser material 13 again. Further, after the laser beam which has been made incident to the laser material 13 passes through the laser material 13 to be optically amplified, it is magnified by the telescope 16 to be propagated to be reflected in the opposite direction to the incident laser beam by the plane reflecting mirror 12 . The laser beam which has been reflected by the plane reflecting mirror 12 is reduced by the telescope 16 to be made incident to the laser material 13 again.
  • the laser beam is further optically amplified by the laser material 13 . That is, the laser beam which has been emitted from the laser material 13 makes a round through the same optical path to be returned back to the laser material 13 to thereby be confined in the laser resonator.
  • the lens interval difference ⁇ in which ⁇ 0 is equal to or smaller than 0.25 mm is obtained is in the range of 2.7 mm to 8.4 mm, and hence it is understood that the stable beam size is obtained over a wide range.
  • ⁇ 1 at this time is in the range of 0.87 mm to 0.49 mm.
  • the stable range is roughly divided into two ranges and also the extent of the stable region becomes narrow. The two regions become away from each other and hence the stable region becomes narrow as the construction of the laser resonator is further deviated from the symmetry. Therefore, the constituent elements of the resonator are arranged roughly in a symmetrical style, whereby the wide stable region can be obtained.
  • FIG. 4 is a schematic view showing the situation of the resonance beam mode when an inclination ⁇ occurs in the plane reflecting mirror 11 , the misalignment occurs between the optical axis 20 of the resonance mode and the optical axis 19 of the laser resonator.
  • the deviation amount of the optical axis in the plane reflecting mirror is d 1
  • the deviation angle of the optical axis in the plane reflecting mirror 11 is ⁇ 1
  • the deviation amount of the optical axis in the resonator center is d 0
  • the deviation angle of optical axis in the resonator center is ⁇ 1 , d 0 , ⁇ 1 , d 1 , and ⁇ 1 are respectively expressed by the following Expression (7).
  • ⁇ 0 and ⁇ 1 are both constant independent of the values of ⁇ , and hence ⁇ 0 is 200 ⁇ rad and ⁇ 1 is 100 ⁇ rad.
  • all of ⁇ 0 , d 0 and ⁇ 0 are not largely changed in the range of L 1 from 0 to 0.05 m.
  • the resonator can be constructed in which even when L 2 ⁇ f 2 , the influence by the inclination of the plane reflecting mirror is insignificant.
  • the telescope having a suitable magnification M can be selected for the resonator length, a stable resonator which ahs a small beam size in spite of the long resonator length can be constructed.
  • a stable resonator can be constructed in which the reduction of the laser output due to the alignment deviation is prevented and also the reduction of the laser beam quality due to the diffraction of the eclipse is prevented.
  • a small laser material can be used in correspondence to a small beam size
  • a laser employing a laser material having a small gain inherent in a material e.g., the laser material, which oscillates with the eye-safe wavelength, such as Er: Glass (the oscillation wavelength is 1.5 ⁇ m), Er, Yb: Glass (the oscillation wavelength is 1.5 ⁇ m), Er: YAG (the oscillation wavelength is 1.6 ⁇ m), Tm: YAG (the oscillation wavelength is 2 ⁇ m), Tm, Ho: YAG (the oscillation wavelength is 2 ⁇ m), Ho: YLF (the oscillation wavelength is 2 ⁇ m), or Tm, Ho: YLF (the oscillation wavelength is 2 ⁇ m), the efficiency of utilizing the laser beam can be enhanced.
  • a polarizer for defining the polarization direction of the laser beam may be arranged either between the plane reflecting mirror 11 and the telescope 15 , or between the plane reflecting mirror 12 and the telescope 16 .
  • a birefringent material such as an EO-Q switch, for carrying out the pulse driving may be arranged either between the plane reflecting mirror 11 and the telescope 15 or between the plane reflecting mirror 12 and the telescope 16 .
  • a laser resonator can be constructed in which the degradation of the extinction ratio of the laser beam becomes less and also the efficiency of utilizing the laser beam is high.
  • FIG. 10 is a schematic view showing the construction of a laser resonator according to Embodiment 2 of the present invention.
  • reference numeral 22 denoted a laser material which has a focal length f r and has the thermal lens effect.
  • Other constituent elements are the same as those in the above-mentioned Embodiment 1.
  • Expression (8) is in the form in which ⁇ in Expression (6) is replaced with ( ⁇ +f 2 2 /2f r ). That is, if the laser material 22 is inserted in the resonator, a resonator can be configured which has a beam size ⁇ 0 that is identical with a beam size before the laser material 22 is inserted in the resonator by changing ⁇ such that ⁇ of the resonator before the insertion and ( ⁇ +f 2 2 /2f r ) after the insertion is the same. In addition, changes in a beam size and an optical axis of a beam due to an inclination of the plane reflecting mirror 11 will be the same before and after the insertion.
  • a stable resonator having a small beam size with a large length can be configured.
  • a stable resonator can be configured in which decrease of a laser output due to misalignment is prevented and degradation of a laser beam quality due to diffraction of an eclipse is also prevented.
  • ⁇ is set as shown in Expression (10) below.
  • ⁇ f 1 2 L 0 - f 2 2 4 ⁇ ( 1 f rx + 1 f ry ) ( Expression ⁇ ⁇ 10 )
  • FIG. 11 is a schematic view showing a configuration of a laser resonator in accordance with Embodiment 3 of the present invention.
  • reference numeral 23 denotes an aperture disposed in a position which is apart from a plane reflecting mirror 11 by a distance L p , and the figure illustrates a state of a resonating beam mode when an inclination ⁇ occurs in the plane reflecting mirror 11 .
  • Other configurations are the same as those in Embodiment 1.
  • a deviation amount d p of an optical axis and a deviation angle ⁇ p of the optical axis in a position of the aperture 23 are represented by Expression (11) shown below.
  • a stable resonator can be configured in which decline of a laser output due to a misalignment is prevented and degradation of a laser beam due to diffraction of an eclipse is prevented.
  • an optical component such as a polarizer, a wave plate, an EO-Q switch, AO-Q switch or the like may be arranged.
  • a stable resonator can be configured in which decline of a laser output due to a misalignment is prevented and degradation of a laser beam due to diffraction of an eclipse is prevented.
  • an output coupling device for taking out a part of a laser may be arranged instead of the aperture 23 .
  • a laser resonator with good stability of an emission position of a laser can be configured.
  • FIG. 12 is a schematic view showing a configuration of a laser resonator in accordance with Embodiment 4 of the present invention.
  • reference numerals 35 and 36 denote plane reflecting mirror
  • reference numeral 37 denotes a telescope having lenses 37 a and 37 b
  • reference numeral 38 denotes a laser material
  • reference numeral 39 denotes an exciting light source for exciting the laser material 38 .
  • the plane reflecting mirrors 35 and 36 are arranged opposing each other, and the laser material 38 is disposed on the side of the plane reflecting mirror 36 .
  • the telescope 37 is arranged between the plane reflecting mirror 35 and the laser material 38 , and a focal length of the lens 37 a of the telescope 37 is fl, a focal length of the lens 37 b of the telescope 37 is f 2 and an interval between the lens 37 a and the lens 37 b is f 1 +f 2 + ⁇ .
  • a distance between the lens 37 a and the plane reflecting mirror 35 is L 1
  • a distance between the lens 37 b and the plane reflecting mirror 36 is L 2 .
  • a laser beam emitted from the laser material 38 to the direction of the telescope 37 is magnified by the telescope 37 and propagated, and is reflected by the plane reflecting mirror 35 to the direction opposite the incident laser beam.
  • the laser beam reflected by the plane reflecting mirror 35 is reduced by the telescope 37 , and is incident in the laser material 38 again.
  • the laser beam incident in the laser material 38 is reflected by the plane reflecting mirror 36 , incident in the laser material 38 again, and is further amplified by the laser material 38 . That is, the laser beam emitted from the laser material 38 goes back and forth the same optical path and returns to the laser material 38 , and is confined in the laser resonator.
  • the effective Fresnel number Nf of the resonator is given in the same manner as in Expression A2.
  • a stable resonator can be configured in which decline of a laser output due to misalignment is prevented and degradation of a laser beam due to diffraction of an eclipse is also prevented.
  • the number of optical components is approximately a half of those shown in FIG. 1, a circulation loss of the resonator is reduced and utilization efficiency of a laser beam can be improved.
  • FIG. 13 is a schematic view showing a configuration of a laser resonator in accordance with Embodiment 5 of the present invention.
  • reference numeral 24 denotes a roof prism having an edge line 24 a that is parallel to the y axis
  • reference numeral 25 denotes a roof prism having an edge line 25 a that is parallel to the x axis.
  • Other configurations are the same as those in Embodiment 1.
  • FIG. 14 is a schematic view showing a reflection state of a laser beam incident on the roof prism 24 of FIG. 13.
  • reflection faces 24 b and 24 c sandwiching the edge line 24 a are fixed perpendicular to each other, and forms an angle of 45 degrees with an optical axis 19 .
  • a laser beam that travels on an optical path 26 parallel to the optical axis 19 and is incident on the roof prism 24 is given changes of direction of a total 180 degrees consisting of 90 degrees by the reflection face 24 b and 90 degrees by the reflection face 24 c .
  • An optical path 27 of the laser beam reflected in this way is also parallel to the optical axis 19 . That is, the roof prism 24 reflects an incident laser beam as a laser beam that is parallel to the incident laser beam and travels in an opposite direction.
  • the roof prism 24 also reflects the incident laser beam as a laser beam that is parallel to the incident laser beam and travels in an opposite direction.
  • the optical paths 26 and 27 are shown as shifted from the optical axis 19 in FIGS. 14 and 15 for illustration purpose, in practice, a center of a beam of either the optical path 26 or the optical path 27 coincides with the optical path 19 , and a laser beam is irradiated on an area including the edge line 24 a and reflected.
  • FIG. 16 is a schematic view showing a configuration of a laser resonator in accordance with Embodiment 6 of the present invention.
  • reference numeral 28 denotes a telescope having lenses 28 a and 28 b
  • reference numeral 29 denotes a telescope having lenses 29 a and 29 b
  • reference numeral 30 denotes a telescope having lenses 30 a and 30 b
  • reference numeral 31 denotes a telescope having lenses 31 a and 31 b .
  • Other configurations are the same as those of the above-mentioned Embodiment 1.
  • a focal length of the lens 28 a of the telescope 28 is f 1
  • a focal length of the lens 28 b of the telescope 28 is f 2
  • an interval between these lenses 28 a and 28 b is f 1 +f 2 + ⁇ 1 .
  • f 1 /f 2 >1.
  • a focal length of the lens 30 a of the telescope 30 is f 3
  • a focal length of the lens 30 b of the telescope 30 is f 4
  • an interval between these lenses 30 a and 30 b is f 3 +f 4 + ⁇ 2.
  • f 3 /f 4 >1.
  • Identical telescopes are used as the telescope 28 shown on the left side of the figure and the telescope 29 shown on the right side, which are arranged in symmetry with a laser material 13 as a center.
  • identical telescopes are used as the telescope 30 shown on the left side of the figure and the telescope 31 on the right side, which are arranged in symmetry with the laser material 13 as a center, and the telescope 30 is arranged between the telescope 28 and the laser material 13 and the telescope 31 is arranged between the telescope 29 and the laser material 13 , respectively.
  • the lens 28 b and the lens 30 a as well as the lens 29 a and the lens 31 a are arranged such that distances between the pairs of lenses are L 2 respectively.
  • the lens 30 b and the resonator as well as the lens 31 b and the resonator are arranged such that distances between the lenses and centers of the resonators are L 3 respectively.
  • a laser beam emitted from the laser material 13 in the direction of the telescope 30 is magnified by the telescope 30 and propagates, and is incident on the telescope 28 .
  • the laser beam incident on the telescope 28 is magnified by the telescope 28 and propagates, and is reflected by the plane reflecting mirror 11 in the direction opposite to the incident laser beam.
  • the laser beam reflected by the plane reflecting mirror 11 is reduced by the telescope 28 and the telescope 30 , and is incident on the laser material 13 again. Moreover, the laser beam incident on the laser material 13 , after passing through the laser material 13 and amplified, is magnified by the telescopes 31 and 29 and propagates, and is reflected by the plane reflecting mirror 12 in the direction opposite to the incident laser beam.
  • the laser beam reflected by the plane reflecting mirror 12 is reduced by the telescope 29 and the telescope 31 , incident on the laser material 13 again, and is further amplified by the laser material 13 . That is, the laser beam emitted from the laser material 13 goes back and forth the same optical path and returns to the laser material 13 , and is confined in the laser resonator.
  • Expression (12) is in the form in which M in Expression (6) is replaced with (M 1 ⁇ M 2 ). That is, if the telescope 30 and the telescope 31 are inserted in the resonator, a size of the resonating mode at the center of the resonator before the insertion is reduced by 1/M 2 times.
  • changes of a beam size and a beam with respect to an optical axis due to an inclination of the plane reflecting mirror 11 maybe found by replacing M in Expression (7) with (M 1 ⁇ M 2 ). That is, a resonating mode of an arbitrary beam size ⁇ 0 can be given by a combination of M 1 and M 2 .
  • a stable resonator having a small beam size with a large length can be configured.
  • a stable resonator can be configured in which decline of a laser output due to misalignment is prevented and degradation of a laser beam due to diffraction of an eclipse is also prevented.
  • the beam size ⁇ 0 in a center of the resonator can be made larger. Therefore, a laser resonator having two kinds of beam sizes ⁇ 0 in one body can be configured. If the beam size ⁇ 0 is changed on the laser material 13 , an output of a laser beam, a beam quality, a pulse width and the like change.
  • a laser resonator with such a configuration, since two kinds of beam sizes of a resonating mode can be given, a laser resonator can be configured in which an output of a laser beam, a beam quality and a pulse width can be changed.
  • the telescope 30 , the telescope 31 , the laser material 13 and the exciting light source 14 may be removed, and a laser material 32 and an exciting light source 33 of different sizes or different materials may be inserted using a replacing apparatus 34 .
  • a laser resonator with such a configuration, since two kinds of beam sizes of a resonating mode can be given to different laser materials, a laser resonator can be configured in which a wave length, an output, a beam quality, a pulse width or the like of a laser beam can be changed.
  • a laser resonator can be configured in which an output of a laser beam, a beam quality and a pulse with in m kinds of ways can be changed.
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CN103762490A (zh) * 2014-01-16 2014-04-30 西安电子科技大学 一种利用热透镜提高光束质量的激光谐振腔的方法

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DE10241988B3 (de) * 2002-09-11 2004-04-08 Tui Laser Ag Diodengepumpter Festkörperlaser mit resonatorinterner thermischer Linse
JP4069894B2 (ja) * 2004-03-30 2008-04-02 三菱電機株式会社 固体レーザ装置

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